sedimentary

Chalcedony (Agate Pebble)

Silicon Dioxide (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 (Mohs); Color: Waxy white to light gray with dark speckles; Luster: Waxy to dull; Structure: Microcrystalline quartz; Specific Gravity: 2.6-2.64.

Hardness: 6
Color: Waxy white to light gray with dark speckles
Luster: Waxy to dull

Identified July 14, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 (Mohs); Color: Waxy white to light gray with dark speckles; Luster: Waxy to dull; Structure: Microcrystalline quartz; Specific Gravity: 2.6-2.64.

Formation & geological history

Formed as a chemical precipitate in cavities of volcanic rocks or sedimentary environments. This specific specimen shows signs of water erosion (alluvial), likely deposited in a stream or river bed during the Quaternary period.

Uses & applications

Commonly used for lapidary work (tumbling/polishing), jewelry (beads), and as an industrial abrasive. Many small specimens like this are collected as decorative pebbles.

Geological facts

Chalcedony is a cryptocrystalline form of silica. The name 'Agate' is specifically used when it shows banding, though many river pebbles are unbanded chalcedony. It was highly prized in antiquity for cylinder seals.

Field identification & locations

Identify by its waxy luster and inability to be scratched by a steel knife. Common in gravel pits, riverbeds, and beaches across North America and Europe. Look for translucency when held to a light source.